Blender Git Loki

add GPU_SHADER_TEXT for font rendering

With USE_GLSL enabled, GPU_basic_shader(TEXTURE|COLOR) always rendered black. New shader uses a solid color + alpha channel of texture (which in our case is a font glyph). See fragment shader for details.

I prefer this approah -- multiple shaders that each do one thing well (and are easy to read/write/understand), instead of one shader that can do many things given the right options.